The invention generally relates to solutions and methods for maintaining the patency of a vascular access device having a lumen and more specifically relates to density-adjusted solutions and the use of such solutions in which the density of the solution is approximately equal to the density of whole blood.
Traditionally, intravenous (I.V.) therapy has been given in a continuous mode. In recent years, for both cost and clinical benefit, methods of intermittent I.V. therapy have been used. In these cases, a catheter or other vascular access device remains in a patient's body continuously, but is periodically detached from traditional I.V. tubing. An anticoagulant combined with a carrier solution is injected into the lumen of the catheter to maintain the patency of the catheter by preventing blood clots from forming in the catheter while it is disconnected from the I.V. tubing.
A typical catheter flush procedure that is used with intermittent I.V. therapy is described below. After proper placement in a patient of a vascular device, such as a catheter, a rubber septum or injection site is attached to the catheter hub permitting ease of access to the catheter lumen without compromising the sterile fluid path. This arrangement is commonly referred to as a "heparin lock".
After the medication has been administered, the catheter injection site assembly is typically flushed with an inert isotonic solution such as physiologic sodium chloride (saline solution). This is done to minimize potential incompatibility problems between the intravenous drug previously administered through the catheter, and the anticoagulant in the carrier solution to be administered.
Traditionally, sodium heparin derived from either pork intestinal mucosa or bovine lung tissue in concentrated strengths of from 1 to 100 units per milliliter in a carrier solution of physiologic saline is administered to the catheter. Flushing volumes of the anticoagulant generally exceed the internal volume of the vascular device to insure total flush. The anticoagulent is administered on an intermittent basis, dependent on the modality of drug therapy, although generally given every eight hours, but not to exceed 24 hours. In this way, it is thought that should blood enter the lumen of the vascular device, the coagulation process will be retarded by the existence of the anticoagulant; thus permitting the catheter to remain patent even when it is in use only on an intermittent basis.
Heparin lock I.V. therapy has experienced significant growth since 1980. Increased clinical popularity can be linked to the following benefits associated with the use of heparin locks: (1) increased ambulatory freedom for patients; (2) general cost containment; and (3) clinical benefits of fluid restriction. Each of these benefits is discussed in greater detail below.
First, normal continuous I.V. therapy requires the patient to remain attached to an intravenous set solution container and I.V. pole. A heparin lock allows the patient to be disconnected from this apparatus, thereby greatly increasing the mobility of the patient.
Second, the use of heparin locks or intermittent drug therapy has been shown to significantly reduce costs. This is due to the fact that simpler intravenous administration sets or syringes can be used to administer drugs through a heparin lock as opposed to more complicated intravenous administration sets designed to be used with multiple containers. Yet another cost savings associated with the use of heparin locks is a reduction in nursing time required to monitor the flow of an I.V. set on a continuous basis as required in more traditional therapies. Yet, another cost savings associated with the use of heparin locks is the complete elimination of the use of pumps or other electrical or mechanical flow control devices to maintain fluid flow through a catheter on a continuous basis.
Third, the use of heparin locks has clinical popularity in patients in which fluid restriction is desired. Oftentimes, intravenous access is required in patients that do not necessarily need intravenous solution or require limited volumes of solution. For example, patients with high blood pressure or other circulatory problems may actually tolerate only limited fluid intake. Traditional continuous I.V. therapy required one liter or more solution per day to maintain catheter patency. A heparin lock completely eliminates the need for continuous fluid administration.
In 1984, approximately 20 million heparin lock procedures were conducted in the U.S. This represents 24% of the total 85 million cannulations given during the same period. Considering a conservative treatment regiment, a cumulative total of 300 million saline heparin flushes were administered during that period. Statistics have indicated a 10% growth rate per year in heparin lock therapy. Over the next ten years, it is estimated that from one-third to one-half of all I.V. therapy will be given by heparin lock.
A great deal has been written in the literature regarding the problem of clot prevention within the lumen of peripheral and central indwelling catheters. Traditionally, extremely low dosing of heparin anticoagulants flushed through the catheter lumen on an intermittent basis has been an effective retardant to clot development in most clinical cases. Nonetheless, as high as 12% of all intermittent sites established continue to be lost due to coagulation buildup and eventual lumen blockage. Attempts to counteract this problem by increasing the dosage, strength, and/or the frequency of administration have not necessarily yielded improved clinical results. In contrast, the risk exists that higher heparin concentrations, volumes or more frequent administrations could increase the likelihood of drug incompatibility reactions with the heparin or, to a much lesser extent, systemic effects on internal physiologic coagulation patterns.
It is important to understand certain fluid dynamic and physiologic factors affecting the initiation of the coagulation cascade in a vascular lumen in a patient, particularly as they relate to the occasional inability to maintain catheter patency regardless of the small heparin dosing schedule used. Assurance of a higher percentage of catheter lumen clear passage could have significant, positive clinical benefit while also affording new options to the development of an antiblocking clot catheter.
To varying degrees based on individual patient hematologic chemistry, fibrinogen layering and, to a lesser extent, platelet aggregation, begin simultaneously with blood entry into the catheter lumen. This is the first stage of the coagulation process. Unfortunately, backflow of blood into the catheter during venipuncture is fundamental to establishing final catheter placement and even though the bulk of the blood is removed by a flushing solution, some fibrinogen layering may have occurred. Subsequent establishment of a minimum fluid flow, or of a static heparin column, serves to retard the chemical reaction between prothrombin and the pre-established fibrinogen layer creating thrombin and the fibrin monomer which eventually polymerizes into clot formation.
In view of the foregoing problems associated with heparin locks, the invention described herein represents an improvement over the traditional use of anticoagulant solutions to maintain the patency of a catheter.